This invention relates to a static controller for power factor correction or adaptive filtering, and more particularly to a cascaded polyphase cycloconverter and single phase high frequency resonant tank circuit controlled so as to provide distribution system power factor correction, either leading or lagging, or alternately to function as a fast response adaptive capacitive filter or inductive filter.
System power factor corrrection in electrical power distribution systems if often required for various lagging loads, and is normally accomplished by polyphase capacitor banks operating at distribution frequency. Also, occasionally a fast system response is required to eliminate damaging resonances in faulted distribution systems or to sufficiently attenuate variable amplitude and/or frequency line harmonics caused by switching type loads. Variable leading reactive power can be obtained by switched capacitor banks, using phase controlled thyristors connected in series with inductors to vary the equivalent reactance. The present invention is directed to an alternate and more versatile solid state circuit that is lightweight with a fast response and provides either power factor correction or adaptive filtering. Both applications are quite common, such as for use with large KVA phase control systems.
The cascaded high frequency link cycloconverter system is disclosed in U.S. Pat. No. 3,742,336 to B. D. Bedford and in allowed application Ser. No. 419,490 now U.S. Pat. No. 3,882,369 to W. McMurray, both assigned to the assignee of this invention, and usually is comprised by input and output cycloconverters separated by a high frequency resonant tank which provides commutation for both cycloconverters. As typically used with an inductive load, the tank frequency is variable to control the amount of reactive power, since the capacitor reactive power increases and the inductor reactive power decreases as the frequency is raised above the resonant frequency. When used without the output cycloconverter as here taught, the high frequency link converter distinguishes in one manner in that only the reactive power needed for power factor correction of filtering is required and not the full load power.